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United States Patent |
6,112,970
|
Takahashi
|
September 5, 2000
|
Continuous atmosphere heat treating furnace
Abstract
So that the brazing of aluminum parts with the use of a flux can be made
effectively without employment of a corrodible metallic muffle, furnace
inner walls made of carbonaceous refractory sheets are utilized as a
brazing space, and an inert atmosphere supplied into this space is
protected from the air by furnace outer walls which are made of steel
sheets to form a furnace shell and which are made hermetical against the
air.
Inventors:
|
Takahashi; Susumu (Yokohama, JP)
|
Assignee:
|
Kanto Yakin Kogyo K.K. (JP)
|
Appl. No.:
|
473086 |
Filed:
|
December 28, 1999 |
Current U.S. Class: |
228/42; 110/336 |
Intern'l Class: |
B23K 001/100; B23K 020/14; F23M 005/00; C21D 001/74; C21D 001/06 |
Field of Search: |
228/214,262.5,46,57,42
110/336
266/255
|
References Cited
U.S. Patent Documents
4154433 | May., 1979 | Kato | 266/255.
|
4193355 | Mar., 1980 | Dondeyne et al. | 110/336.
|
4629423 | Dec., 1986 | Venus | 432/247.
|
5817198 | Oct., 1998 | Viertola | 156/71.
|
5897326 | Apr., 1999 | Eldridge et al. | 438/14.
|
Primary Examiner: Ryan; Patrick
Assistant Examiner: Newsome; C.
Attorney, Agent or Firm: Shlesinger Fitzsimmons Shlesinger
Parent Case Text
This application is a division of my co-pending application Ser. No.
09/135,450, which was filed Aug. 17, 1998.
Claims
What is claimed is:
1. An elongate continuous atmosphere furnace for heat treatment including
aluminum brazing which comprises an elongated heating space extending in a
longitudinal direction of the furnace and formed by walls made of
carbonaceous refractory materials, and metallic outer shells surrounding
the walls with insulation positioned between the walls and outer shells
and hermetically sealing the heating space from air.
2. The furnace as defined in claim 1, which further comprises heating
elements in the furnace, parts of which are hermetically fitted to the
outer shells, and wherein the elongated heating space is made of
carbonaceous refractory plates, those of which laid at the bottom of the
space forming a hearth cut transversely to the longitudinal direction of
the furnace and divided into a desired number of pieces.
Description
BACKGROUND OF THE INVENTION
This invention relates to a method of brazing aluminium or aluminium alloy
parts, and more particularly the method of brazing them with a flux.
The invention also relates to an atmosphere furnace which can
advantageously be employed for such brazing method.
When iron, copper, or their alloys are put into a furnace employing as its
atmosphere a reductive gas such as hydrogen and carbon monoxide, and are
subjected to a high temperature, they are deoxidized. Therefore, the
brazing of such metals within such atmosphere furnace does not need a
flux.
On the other hand, as aluminium and its alloys are not deoxidized even
under an extremely low partial pressure of oxygen, they can not be brazed
by heating them within the atmosphere furnace of the kind mentioned above.
Accordingly, their brazing has been made not by an atmosphere but by the
use of a flux.
Conventional brazing may be summarized that the brazing of iron, copper, or
their alloys by heating them within a furnace employs a reductive
atmosphere but does not need a flux, while the brazing of aluminium and
its alloys does employ a flux but does not need a reductive atmosphere.
On the contrary to the above-summarized conventional brazing methods, it
becomes lately useful or essential for brazing, with a flux, aluminium and
its alloys to employ an inert atmosphere, too. This is in order to braze
aluminium parts with a minimum amount of flux and effectively without
causing environmental pollution.
To wit, as those fluxes which are commonly used for brazing aluminium parts
and have a melting point of 500-550.degree. C., are made from fluorine
compounds such as aluminium fluoride, potassium tetrafluoroaluminate,
sodium fluoride, and so on, or alkali metal chloride containing one or
more fluorine compounds, they are soluble only slightly in water, and
accordingly it needs a large volume of water to wash off them. In order to
reduce the volume of water for washing off them or to eliminate a washing
step in view of environmental pollution, they must be used as minimum as
possible.
While the reduction of use of fluxes can be against environ-mental
pollution, especially water pollution, it can be economic too. It can
yield fine aluminium articles with little flux residues. It can prevent a
furnace from being eroded much by fluxes.
However, fluxes which have been applied over aluminium parts thinly in
order to minimize them, are readily oxidized at a high temperature.
Oxidized fluxes of the kind mentioned above will have a melting point more
than 1,000.degree. C. Since a melting point of Al--Si system solders which
are commonly used in aluminium brazing, is about 500-630.degree. C., and
since the aluminium or aluminium alloy brazing is conducted at about
580-660.degree. C., the oxidized fluxes having the melting point as high
as 1,000.degree. C. are unserviceable. They will induce secondary
oxidation of aluminium or aluminium alloy parts, to which they have been
applied.
Consequently, even in the brazing of aluminium or aluminium alloy parts,
heating them under an inert atmosphere becomes essential, as described
above, in order to prevent fluxes from oxidizing. In practice, a hermetic
metallic muffle filled up with nitrogen gas of a high purity is installed
in a furnace, and the aluminium or aluminium alloy parts are brazed with a
flux under an inert atmosphere within the metallic muffle.
While such metallic muffle protects its atmosphere from an outer
disturbance, electric heating elements which are installed in a space
between the muffle and inner furnace walls, are protected by the muffle
from fluxes scattered therein, whereby the muffle prevents the heating
elements from troubling electrically on account of the fluxes. Although
metallic muffles work so, it is not easy to replace them when they are
damaged by fluxes and so on. As metallic muffles employed today are as
long as 10 m, it is laborious to install or replace them.
It is therefore an object of this invention to provide a method of
continuously brazing aluminium or aluminium alloy parts with the use of
fluxes and under an inert atmosphere such as nitrogen within a furnace
which does not employ any metallic muffle, and to provide also the furnace
which can carry out the method well.
SUMMARY OF THE INVENTION
In this invention, the air is excluded from an inert atmosphere which is
within a furnace and prevents the oxidation of aluminium or aluminium
alloy parts assembled and applied with solders and fluxes for brazing,
particularly the oxidation of the fluxes, not by the aforementioned kind
of conventional hermetic metallic muffle installed within the furnace, but
by metallic outer walls which are outside of furnace inner walls through
insulations to form hermetic shells, whereby the inert atmosphere
introduced directly into a space within the furnace inner walls and
filling up the space is protected from the air.
In this invention, apparatuses, devices; and tools which penetrate through
the metallic outer shell walls and furnace inner walls and are installed
so as to open or face in the furnace inner walls, such as for example
atmosphere gas supplying tubes, thermometers, heating elements, atmosphere
observation meters, and the like, are also provided hermetically against
the air.
Since inorganic bases contained in the aforementioned kind of fluxes
severely erode oxide refractories, it is preferable to build the furnace
inner walls by carbonaceous refractories which stand well against such
erosion. And, it is preferable also to have a bottom of furnace inner
walls, viz., the hearth divided into several pieces transversely to the
longitudinal direction of the hearth, so that the divided hearth may be
pushed or drawn out longitudinally for inspecting it or replacing required
pieces of the hearth.
THE DRAWINGS
FIG. 1 is an explanatory sectional view of an essential part of a
continuous atmosphere furnace which can advantageously be employed to
practice this invention method.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
First, a furnace which can advantageously be employed for practicing the
method of this invention, is explained with reference to FIG. 1.
Furnace inner walls 1 which are sheets made by sintering pure graphite, one
of carbonaceous materials, form a tunnellike space which extends along a
longitudinal direction of the furnace and is rectangular in its
cross-section, and in which a brazing operation is made. The furnace inner
walls indicated by 1' are bottom walls which form a hearth of the furnace
and are divided transversely to the longitudinal direction of the furnace
into a desired number of pieces.
Steel sheets 2' which form a furnace shell located outside of the furnace
inner walls 1 with insulations 2 therebetween, are made hermetical against
the air. Numerals 3 indicate a pair of electric resistant heaters having
heating elements 4 located within the furnace inner walls 1 and also
having outer ends which penetrate through the furnace shell sheets 2' and
are hermetically sealed against the air by a hermetic boxes 6. The heating
elements 4 of the heaters 3 are covered by ceramic sleeves 5 so that their
insulation shall not be damaged by fluxes scattering within the furnace
inner walls. Ceramics may be replaced by metallic materials and so on
which are anticorrosive against fluxes.
A conveyor 7 which circulates through the rectangular space within the
furnace inner walls 1 in the longitudinal direction of the furnace for
carrying aluminium parts, is preferably made by carbonaceous materials.
Apparatuses which penetrate through the shell sheets 2' and furnace inner
walls 1 and are installed so as to open or locate within the furnace inner
walls, such as atmosphere supplying tubes, thermometers, atmosphere
observation meters, and the like which are not shown in the drawing, are
also made hermetical against the air, similarly to the heaters 3.
EXAMPLE 1
Directly into a space (650 mm in width, 6,000 mm in length, and 180 mm in
effective height) made by the furnace inner walls 1 of the above-described
continuous atmosphere furnace, a nitrogen gas of a high purity was sent by
33 m.sup.3 /hour from an atmosphere supplying tube open at its central
upper portion (not shown). At the same time, into the hermetical sealing
boxes 6 too, the nitrogen gas was charged. The space made by the furnace
inner walls 1, that is, a heating chamber was kept at 600.degree. C. by
the heaters 3.
Into the heating chamber, assemblies of aluminium parts were sent by the
conveyor 7 at a rate of 60 assembly/hour. Each assemblies was adhered with
60 g of a flux made from alkali metal chloride containing fluorine
compounds and having a melting point of 547.degree. C. and was coated by
an Al--Si system brazing sheet of a melting point of 590.degree. C.
Although the nitrogen gas supplied into the heating chamber was gradually
discharged to the outside from inlet and outlet openings, air did not
enter into the chamber, and the furnace atmosphere was always kept at an
oxygen amount of 25-55 ppm. Brazing was conducted very well for a long
period of time.
In this invention, without employing a corrodible metallic muffle, the
brazing with a flux of aluminium or aluminium alloy parts is performed
under a desired atmosphere, whereby the brazing becomes economic in its
operation and maintenance. It is a characteristic feature of this
invention that as hermetic means which shut the furnace from the air, are
located remotely from its heating chamber, the means shall not be
subjected to a high temperature and will not be eroded by fluxes. As they
are furnace shells and sealing boxes attached to the shells, materials and
structures by which they are made, can be selected rather freely, and
their maintenance will be comparatively easy.
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